AVS 66th International Symposium & Exhibition
    Thin Films Division Tuesday Sessions
       Session TF+PS-TuA

Paper TF+PS-TuA12
The Role of Template Layers in Heteroepitaxial ALD Growth of Crystalline La2O3 on GaN(0001)

Tuesday, October 22, 2019, 6:00 pm, Room A124-125

Session: Epitaxial Thin Films
Presenter: Pei-Yu Chen, University of Texas at Austin
Authors: P.Y. Chen, University of Texas at Austin
T. Hadamek, University of Texas at Austin
S. Kwon, University of Texas at Dallas
F. Al-Quaiti, University of Texas at Austin
A. Posadas, University of Texas at Austin
M.J. Kim, University of Texas at Dallas
A.A. Demkov, University of Texas at Austin
J.G. Ekerdt, University of Texas at Austin
Correspondent: Click to Email
The high switching frequency, operating temperatures and voltages make GaN the material of choice for higher power applications and instrumental to reducing power consumption. In many of these applications, there is a need for a high quality gate dielectric. Lanthanum sesquioxide, La2O3, is one of the promising gate insulator candidates. In this work, we compare La2O3 thin films grown by atomic layer deposition (ALD) and molecular beam epitaxy (MBE), and explore the formation of ALD-La2O3 films on GaN(0001). An island growth mode (Volmer-Weber growth) was observed when La2O3 films were deposited directly on GaN(0001) at 250 °C by ALD using tris(N,N’-diisopropylformamidinato)-lanthanum as the precursor and H2O as the co-reactant. Only with use of a thin template layer, 2 nm-thick hexagonal La2O3 grown by MBE or 3 nm-thick cubic Er2O3 grown by ALD, can a 2-dimensional ALD-La2O3 thin film be formed. The 2-dimensional ALD-La2O3 growth on templated-GaN(0001) was confirmed by RHEED and AFM. The macrostructure and microstructure of ALD-La2O3 films were verified with XRD, STEM, and atomic structure modeling. The ALD-La2O3 film retains a cubic structure on ALD-Er2O3 templated-GaN(0001) while it transforms from the cubic phase to mixture of cubic and hexagonal phases on MBE-La2O3 templated-GaN(0001) when the film is thicker than 15 nm. Hexagonal La2O3 is more thermodynamically stable than cubic bixbyite La2O3; the stabilization of cubic ALD-La2O3 on ALD-Er2O3 templated-GaN(0001) can be attributed to the use of the cubic ALD-Er2O3 template and relatively low growth temperature. Analogies are presented for the In2O3 system, which has similar cubic bixbyite and hexagonal structures as La2O3, except the phases are reversed in In2O3. We calculate the surface energy of hexagonal In2O3 and compare the result with reported cubic In2O3 values to explore the relative contribution of bulk and surface energies in stabilizing the structure of thin crystalline films. Stabilization of thin cubic ALD-La2O3 on hexagonal MBE-La2O3 templated-GaN(0001) is attributed to likely surface energy differences between cubic and hexagonal La2O3.